1. Field of the Invention
The present invention relates to a fluid transmitting device such as a torque converter, a fluid coupling and the like used in a power transmitting system of a vehicle and an industrial machine, and particularly to a fluid transmitting device with a lock-up clutch, which includes a pump impeller, a turbine runner defining a circulation circuit between the turbine runner itself and the pump impeller, a side cover connected to the pump impeller and defining a clutch chamber between the side cover itself and an outer surface of the turbine runner to communicate with an outer periphery of the circulation circuit, and a lock-up clutch disposed in the clutch chamber and capable of connecting the side cover and the turbine runner directly to each other, the lock-up clutch comprising a clutch piston axially movably connected to the turbine runner to divide the clutch chamber into an inner oil chamber on the side of the turbine runner and an outer oil chamber on the side of the side cover, a lock-up control means adapted to generate a difference in pressure between the inner oil chamber and the outer oil chamber in order to advance and retract the clutch piston toward and away from an inner surface of the side cover, and a friction engaging means for bringing the clutch piston and the side cover into friction engagement with each other, when the clutch piston is urged toward the inner surface of the side cover.
2. Description of the Related Art
A conventional fluid transmitting device with a lock-up clutch is known as disclosed in, for example, Japanese Patent Application Laid-open No. 5-296313.
In general, in the conventional fluid transmitting device with the lock-up clutch, a dragging-preventing gap is provided between the clutch piston and the side cover in a non-connected state of the lock-up clutch. Therefore, when the lock-up control means is operated to bring the lock-up clutch into a connected state, working oil is more or less leaked from the high-pressure inner oil chamber through the gap into the low-pressure outer oil chamber at an initial stage of the operation of the lock-up control means. This is one factor of the retardation in the operation of the lock-up clutch.
In order to eliminate the retardation in the operation of the lock-up clutch, in the fluid transmitting device disclosed in the above-described publication, a seal member is mounted on an outer periphery of the clutch piston to come into a close contact with an inner peripheral surface of the side cover, thereby preventing the leakage of the working oil. This fluid transmitting device has the following problems: It is required that a one-way valve is provided in the clutch piston in order to enable the working oil from the outer oil chamber to flow toward the inner oil chamber upon the release of the operation of the lock-up clutch, inevitably leading to an increase in the number of parts and in turn an increase in cost; in addition, the seal member on the outer periphery of the clutch piston always rubs against the inner peripheral surface of the side cover, when the pump impeller and the turbine runner are rotated relative to each other in the non-connected state of the lock-up clutch, so that it is difficult to ensure the durability of the seal member.
Accordingly, it is an object of the present invention to provide a fluid transmitting device with a lock-up clutch, wherein the connection responsiveness of the lock-up clutch is excellent, and moreover the number of parts is small, leading to a lower cost, and the durability is high.
To achieve the above object, according to a first feature of the present invention, there is provided a fluid transmitting device with a lock-up clutch, which includes a pump impeller, a turbine runner defining a circulation circuit between the turbine runner itself and the pump impeller, a side cover connected to the pump impeller and defining a clutch chamber between the side cover itself and an outer surface of the turbine runner to communicate with an outer periphery of the circulation circuit, and a lock-up clutch disposed in the clutch chamber and capable of connecting the side cover and the turbine runner directly to each other; the lock-up clutch comprising a clutch piston axially movably connected to the turbine runner to divide the clutch chamber into an inner oil chamber on the side of the turbine runner and an outer oil chamber on the side of the side cover, a lock-up control means adapted to generate a difference in pressure between the inner oil chamber and the outer oil chamber in order to advance and retract the clutch piston toward and away from an inner surface of the side cover, and a friction engaging means for bringing the clutch piston and the side cover into friction engagement with each other, when the clutch piston is urged toward the inner surface of the side cover; wherein the device includes a dividing means provided between the turbine runner and the clutch piston for dividing the inner oil chamber into a radially inner and substantially closed primary inner oil chamber section and a radially outer secondary inner oil chamber section, when the clutch piston occupies a retracted position in which at least the friction engaging means is inoperative, so that when the lock-up control means is operated to urge the clutch piston in a direction of engagement of the friction engaging means, the pressures in the primary inner oil chamber section and the secondary inner oil chamber section are raised in the named order relative to the outer oil chamber.
With the first feature, when the lock-up control means is operated to urge the clutch piston in the direction of engagement of the friction engaging means, the pressures in the primary inner oil chamber section and the secondary inner oil chamber section are raised in the named order relative to the outer oil chamber. Specifically, the clutch piston can be first advanced in a direction to operate the friction engaging means by the quick raising of the pressure in the primary inner oil chamber section, thereby inhibiting the leakage of the working oil from the secondary inner oil chamber section to the outer oil chamber. Thus, the raising of the pressure in the secondary inner oil chamber section can be also hastened, and as a result the raising of the pressures in the primary inner oil chamber section and the secondary inner oil chamber section as a whole can be hastened, whereby the clutch piston can be urged quickly and powerfully toward the side cover to enhance the connection responsiveness of the lock-up clutch. Moreover, the urging force on the clutch piston is sequentially generated in the primary inner oil chamber section and the secondary inner oil chamber section, whereby the shock of the connection of the lock-up clutch can be alleviated.
In the disconnected state of the lock-up clutch, a relative rotation does not occur in the dividing means, and hence the durability of the dividing means can be ensured.
Further, in the disconnected state of the lock-up clutch, the flowing of the working oil from the outer oil chamber to the inner oil chamber can be conducted smoothly without recourse to a one-way valve required in the prior art, and the cooling of the lock-up clutch can be achieved. In addition, the number of parts can be reduced because no one-way valve is required, to thereby contribute to a reduction in cost.
According to a second feature of the present invention, in addition to the first feature, a through-bore is provided in the turbine runner to permit the primary inner oil chamber section to communicate with the circulation circuit.
With the second feature, during the decelerating operation of the fluid transmitting device in which the turbine runner is in a position to drive the pump impeller, the pressure in an area of the circulation circuit on the side of the turbine runner becomes high, whereby the working oil flows from the circulation circuit through the through-bore into the primary inner oil chamber section to raise the pressure in the primary inner oil chamber section. Therefore, when the lock-up control means is operated to urge the clutch piston in the direction of engagement of the friction engaging means, the raising of the pressures in the primary and secondary inner oil chamber sections can be hastened as a whole in correspondence to an increment in already raised pressure in the primary inner oil chamber section, and hence the connection responsiveness of the lock-up clutch can be further effectively enhanced.
During the accelerating operation in which the pump impeller is rotated at a speed higher than the turbine runner, the pressure in the area of the circulation circuit on the side of the turbine runner is lower, and hence the working oil in the primary inner oil chamber section flows through the through-bore into the circulation circuit to lower the pressure in the primary inner oil chamber section, but the dropping of the pressure in the primary inner chamber section does not involve the secondary inner chamber section, because the through-bore does not communicate with the secondary inner chamber section and moreover, the primary and secondary inner chamber sections are partitioned from each other by the dividing means. Moreover, the secondary inner chamber section is maintained at a relatively high pressure, because it communicates with the outer periphery of the circulation circuit. Therefore, when the lock-up control valve is operated to bring the lock-up clutch from this state into the connected state, the clutch piston is operated in the direction of engagement of the friction engaging means by a difference in pressure between the high-pressure secondary inner chamber section and the low-pressure outer chamber, whereby the lock-up clutch can be brought into the connected state without hindrance.
The fluid transmitting device corresponds to a torque converter T in each of embodiments of the present invention which will be described hereinafter; the friction engaging means corresponds to a friction surface 5b and a friction lining 28, and the lock-up control means corresponds to a lock-up control valve 42.